TC redesigned the cock which can improve the ignition and allows for much greater longevity of the flint.
Blue ones are available from TC which are made to fit all of the standard size TC flint locks.
Notice in the photo below how the shape of the new style cock has slightly less of an "S" shape to it which improves the lock geometry:
http://www.thetruthaboutguns.com/201...ter-firestorm/
Some folks also install an improved vent liner.